1. Field of the Invention
The present invention relates to a small brush motor of a four-magnetic-pole-six-salient pole structure provided with a varistor for suppressing overvoltage, and more particularly, to the winding state of an armature coil winding.
2. Description of the Related Art
As seen in Japanese Unexamined Patent Publication (Kokai) No. 11-69747, U.S. Pat. No. 6,153,960, and U.S. Pat. No. 6,285,109, in small brush motors of four-magnetic-pole-six-salient pole structures, motors are being increased in flatness, reduced in size, reduced in cost, and reduced in wiring defects by using three-electrode ring varistors usually used for two-magnetic-pole-three-salient pole structures as varistors for suppressing overvoltage (extinguishing spark arcs). For this, it is necessary to electrically connect the opposed risers in a point symmetric positional relationship about the center of rotation of the armature core among the six risers (terminal parts of commutator pieces). For the purpose of improving the productivity, etc., instead of using special printed circuit boards for connecting the risers or using the known commonly applied art of individual wiring using conductors, they are connected by using partial segments of the coil wrapped around the six salient poles so as to achieve a continuous pattern including the six risers.
That is, the armature 10 of this small brush motor, as shown in FIGS. 7A and 7B, is provided with a shaft 12, an armature core 11 having six salient poles P1 to P6 in a radial array, a commutator 15 having six risers R1 to R6 positioned between the salient poles at one end face of the armature core 11, a three-phase coil 17 comprised of a single wire continuously wound around the six risers R1 to R6 and the six salient poles P1 to P6 in the form of a continuous pattern, a ring varistor 19 for suppressing overvoltage having three electrodes (19a, 19a, 19a) connected to every other one of the six risers R1 to R6, that is, three risers (R2, R4, and R6), and a brush (not shown) for sliding contact with the commutator 15. Further, this small motor is provided with a stator permanent magnet (not shown) having four magnetic poles.
Each phase coil of the three-phase coil 17 is obtained by winding the wire around a first riser (R1, R3, and R5) and a second riser (R2, R4, and R6) in a point symmetric positional relationship with respect to the center of rotation of the armature core 11, then winding around the first salient pole (P1, P3, and P5) adjoining the second riser, then winding around a second salient pole (P2, P4, and P6) in a point symmetric positional relationship with the first salient pole (P1, P3, and P5) about the center of rotation of the armature core 11. Each phase coil is attached using three risers and two salient poles.
Here, as shown by spreading open the peripheral end of the armature core in FIG. 8A, a first phase coil is comprised by knotting a winding start S to the riser R1, winding the wire in the forward rotation direction (arrow direction), knotting it with the riser R4 opposed to the riser R1 in a point symmetric positional relationship about the center of rotation of the armature core 11, wrapping it around the adjoining salient pole P1 in the forward rotation direction as the first coil part C11, then winding it in the reverse rotation direction and wrapping it around the salient pole P2 opposed to the salient pole P1 as the second coil part C12, then winding it in the reverse direction rotation and knotting it with the adjoining riser R3 in the forward rotation direction of the salient pole P1. Next, the second coil is comprised by winding the wire in the reverse rotation direction from the riser R3, knotting it with the riser R6 opposed to the riser R3, wrapping it around the adjoining salient pole P3 in the forward rotation direction as the first coil part C21, then winding it in the reverse rotation direction and wrapping it around the salient pole P4 opposed to the salient pole P3 as the second coil part C22, then winding it in the reverse direction rotation and knotting it with the adjoining riser R5 in the forward rotation direction of the salient pole P3. Next, the third phase coil is comprised by winding the wire in the forward rotation direction from the riser R5, knotting it with the riser R2 opposed to the riser R5, wrapping it around the adjoining salient pole P5 as the first coil part C31 in the forward rotation direction, then winding it in the forward rotation direction and wrapping it around salient pole P6 opposed to the salient pole P5 as the second coil part C32, then knotting it with the adjoining riser R4 in the forward rotation direction as the winding end E. Here, if expressing the forward rotation direction by the arrow mark xe2x86x92, the reverse direction rotation by the arrow mark , and the length of the crossover wire between the salient poles, between the risers, and between a salient pole and a riser by rotational angle (radians) as a general measure and showing the winding order by simple symbols, the result becomes as follows:
Winding state shown in FIG. 8A:
R1(S)(xcfx80)xe2x86x92R4xe2x86x92(xcfx80/6)xe2x86x92P1(xcfx80)P2(xcfx80/3)R3(xcfx80)xe2x86x92(xcfx80/6)xe2x86x92P3(xcfx80)P4(xcfx80/3)R5xe2x86x92(xcfx80)xe2x86x92R2xe2x86x92(xcfx80/6)xe2x86x92P5xe2x86x92(xcfx80)xe2x86x92P6xe2x86x92(xcfx80/6)xe2x86x92R4(E) 
FIGS. 8B and 8C show other continuous patterns.
Winding state shown in FIG. 8B:
R1(S)xe2x86x92(xcfx80)xe2x86x92R4xe2x86x92(xcfx80/6)xe2x86x92P1xe2x86x92(xcfx80)xe2x86x92P2xe2x86x92(xcfx80/6)xe2x86x92R6xe2x86x92(xcfx80)xe2x86x92R3xe2x86x92(7xcfx80/6)xe2x86x92P3xe2x86x92(xcfx80)xe2x86x92P4xe2x86x92(xcfx80/6)xe2x86x92R2xe2x86x92(xcfx80)xe2x86x92R5xe2x86x92(7xcfx80/6)xe2x86x92P5xe2x86x92(xcfx80)xe2x86x92P6xe2x86x92R4(E) 
Winding state shown in FIG. 8C:
R1(S)xe2x86x92(7xcfx80/6)xe2x86x92P1(xcfx80/6)R4xe2x86x92(xcfx80/6)xe2x86x92P1(xcfx80)P2(5xcfx80/6)R3xe2x86x92(xcfx80/6)xe2x86x92P4(7xcfx80/6)R6xe2x86x92(xcfx80/6)xe2x86x92P3(xcfx80)P4xe2x86x92(5xcfx80/6)R5(E) 
Summarizing the problems to be solved by the present invention, even with the small brush motor of the above four-magnetic-pole-six-salient-pole structure, greater flatness, smaller size, and higher torque are being demanded. As a motor is made flatter and smaller, however, the coil area per salient pole also becomes smaller and increasing the torque becomes difficult. In general, there is a tradeoff between greater flatness and smaller size and higher torque. In general, along with greater flatness and smaller size, the coil has to be made finer, but with a single coil, if the number of turns is increased, the wire length will become longer, so the resistance loss (copper loss) will become greater. As a means for easing this to some extent, if winding a coil comprised of N (natural number) number of ultrafine wires arranged in parallel by a continuous pattern, at the coil part at each salient pole, as compared with winding a single ultrafine wire as the coil in a continuous pattern, the wires become denser and the coil area can be increased to a certain extent and also the copper loss can be suppressed using the surface film effect due to the relative increase in the surface area of the wires. Therefore, even with greater flatness and smaller size, the torque can be increased to a certain extent.
In general, however, when using ultrafine wire as the coil, the tensile strength becomes considerably weaker and disconnection easily occurs, so it is necessary to shorten the length of crossover wires between salient poles, between risers, and between risers and salient poles as much as possible. Further, when fixing wires conductively by soldering, etc., to the knotting parts of the risers R1 to R6, the heat of melting is conducted from the risers to the crossover wires, so it is necessary to eliminate cross points between crossover wires between different phase coils and prevent short-circuits between different phase coils due to destruction of the insulating films of the crossover wires. If there is a cross point of crossover wires near risers between coils having the same phase, while there is no problem even with point peeling of the insulating film at the time of manufacture, the conductive wires will abrade as a result of rubbing due to vibration or the thermal cycle while driving the motor, and disconnection accidents are liable to occur, so it is preferable that there are no cross points of the crossover wires near the risers.
The brush-type motor of the above four-magnetic-pole-six-salient-pole structure, however, suffers from the following problems:
(1) In the winding state shown in FIG. 8A, there are crossover wire lengths exceeding the distance between adjoining salient poles (xcfx80/3) such as the crossover wire a1 from the riser R1 to the riser R4 and the crossover wire a2 from the salient pole P1 to the salient pole P2. Further, there are cross points of the crossover wires between different phase coils near the risers such as the cross point between the crossover wire a3 from the riser R4 to the salient pole P1 and the crossover wire a4 from the riser R3 to the riser R6, so disconnection or a short-circuit is liable to occur. In this winding state, if the order of the winding direction of the first phase coil is applied to the second phase coil, the wire should be knotted with the riser R6 and wrapped around the adjoining salient pole P2 in the reverse rotation direction, but in actuality part of the order of winding direction of the first phase coil is broken and the wire is knotted with the riser R6 and wrapped around the adjoining salient pole P3 in the forward rotation direction. The breakage in the order occurs in the third phase coil as well, and there is a cross point of the crossover wires near the riser R4 of the winding end E.
(2) In the winding state shown in FIG. 8A, there are crossover wire lengths exceeding the distance between adjoining salient poles (xcfx80/3) such as the crossover wire a1 from the riser R1 to the riser R4 and the crossover wire a2 from the salient pole P1 to the salient pole P2. Further, there are cross points of the crossover wires between different phase coils near the risers such as the cross point between the crossover wire a3 from the riser R4 to the salient pole P1 and the crossover wire a4 from the riser R3 to the riser R6, so disconnection or a short-circuit is liable to occur. In this winding state, if the order of the winding direction of the first phase coil is applied as it is to the second phase coil and the third phase coil, the winding directions of the crossover wires between the risers and between the salient poles are uniformly the forward rotation direction from the winding start S to the winding end E, so the total length of the crossover wires becomes rather long. If the winding order is uniformly used in the coils of all phases, cross points will occur between the crossover wire a1 and the crossover wire a5 of the riser R6 from the salient pole P1.
(3) In the winding state shown in FIG. 8C, the winding order is made uniform for the coils of all of the phases, but the winding directions between the risers and the winding directions between the salient poles are opposite to each other. There are no cross points between crossover wires of different phase coils. For example, the crossover wire a3 from the riser R4 to the salient pole P1 and the crossover wire a4 from the riser R3 to the riser R6 do not cross. The reason is that the crossover wire a4 is not passed between the salient poles P6 and P1, but is made to bypass them by attachment to the salient pole P4. However, there are cross points of crossover wires near the risers between same phase coils. Further, for example, there are lengths of crossover wires exceeding the distance (xcfx80/3) between adjoining salient poles and disconnection is liable to occur such as at the crossover wire a1 from the riser R1 to the salient pole P3 or the crossover wire a2 from the salient pole P1 to the salient pole P2.
In each of these winding states, it is necessary to attach the wire at the adjoining salient pole P3 or salient pole P5 serving as a loose stopper immediately before winding around the salient pole P2. Further, because the coil at the salient pole P1 and the coil at the salient pole P2 have the same winding direction, it is not possible to wind the wire around the salient poles between them alternately at the crossover wire a2 from the salient pole P1 to the salient pole P2, resulting in lengths of crossover wires exceeding the distance (xcfx80/3) between adjoining salient poles. Further, because there are cross points of the crossover wires near the risers, the conductive wires will abrade due to rubbing as a result of vibration or the thermal cycle while driving the motor and disconnection accidents are liable to occur.
An object of the present invention is to provide a small brush motor which uses as an overvoltage suppressing varistor a three-electrode ring varistor as generally used in an armature of a two-magnetic-pole-three-salient pole structure and which improves the winding state of the coils so as to suppress occurrence of disconnection or short-circuits of crossover wires.
To attain the above object, there is provided a small brush motor comprised of an armature core having six salient poles in a radial array, a commutator having six risers positioned between the salient poles at one end face side of the armature core, a three-phase coil knotted with the six risers and wrapped around the salient poles, an overvoltage suppressing varistor connected to the risers, a brush in sliding contact with the commutator, and an outer permanent magnet having four magnetic poles, each phase coil of the three-phase coil being attached using three risers and two salient poles.
Here, assume the side opposite to the one end face side of the armature core is xe2x80x9cthe other end face sidexe2x80x9d. Further, assume the risers in a point symmetric positional relationship about the center of rotation of the armature core among the six risers are referred to as first risers and second risers, respectively. The first risers are not connected to the electrodes of the overvoltage suppressing varistor. The second risers are connected to the electrodes of the overvoltage suppressing varistor. Still further, assume the salient poles adjoining each other in the forward rotation direction and reverse rotation direction among the six salient poles are referred to as first salient poles and second salient poles, respectively. That is, in the present invention, each phase coil has a zigzag part, a first coil part and a second coil part. The zigzag part is formed by alternately bending and connecting the three salient poles in the interval from the knotting part (wrapped part) of the first riser in the forward rotation direction to the knotting part of the second riser successively to the other end face side, the one end face side, and the other end face side. The first coil part is formed by winding from the knotting part of the second riser in the reverse rotation direction and wrapping around the adjoining first salient pole. The second coil part is formed by winding from the first coil part in the forward rotation direction and wrapping at the adjoining second salient pole and winds from the first coil part in the forward rotation direction and connects to the first riser of an adjoining different phase. The winding directions of the first coil part and the second coil part are opposite winding directions from each other.
Because the first coil part and the second coil part of the same phase coil are formed wound oppositely at the adjoining first and second salient poles, the interval from the knotting part of the first riser in the forward rotation direction to the knotting part of the second riser can be formed as a zigzag part successively alternately bending the three salient poles to the other end face side, the one end face side, and the other end face side. Further, the first coil part can be wrapped from the knotting part of the second riser adjoining it and can be knotted with the opposite phase first riser adjoining it from the second coil part, so the total length of all crossover wires in the coil can be kept to not more than the distance (xcfx80/3) between salient poles and occurrence of disconnection can be suppressed. Further, it is, possible to eliminate the cross points of crossover wires connecting the knotting part of the riser and coil part of the salient pole between different phase coils, so when soldering or otherwise fixing the knotting parts of the risers, even if the heat of melting is conducted to the crossover wires, because there are no cross points of the crossover wires between different phase coils, it is possible to prevent destruction of the insulation film of the crossover wires, possible to prevent short-circuits between different phase coils, and reduce the size and improve the yield of the motors. Further, the total length of the crossover wires serving as relay wires can be shortened, so the copper loss can be suppressed.
In the same phase coil, while there are cross points between the two crossover wires for the knotting parts of the risers (knotting start wire and knotting end wire) and peeling of the insulating film may occur and short-circuits arise due to the heat of melting at the time of manufacture without problem, the uncovered conductive wires are liable to abrade and disconnection accidents occur at the cross points due to vibration occurring during motor operation. The point is even more important when the wires are ultrafine wires.
Therefore, preferably the winding directions of the knotting part of the second riser and the first coil part are the same direction and the winding directions of the second coil part and the knotting part of the first riser of the different phase are the same direction. According to this winding state, the two crossover wires are bent outward, so no cross point is generated, the occurrence of disconnection accidents is suppressed, and a high reliability motor can be provided.
Note that the coil may be made one comprised of a plurality of ultrafine wires arranged in parallel or a single ultrafine wire.